A device of this type is described in the journal SPIE, Vol. 907, Laser Surgery: Characterization and Therapeutics, 1988, S. Albin et al., "Laser Induced Fluorescence of Dental Caries", pages 96 to 98. In the known device, a laser emits monochromatic radiation towards the tooth, and this induces fluorescent radiation. From carious places of the tooth there is issued fluorescent radiation which is characteristic of caries and differs from the returned radiation of a healthy tooth in its intensity and spectral distribution. The returned radiation is observed using a filter. The places of the tooth affected by caries appear as dark spots during observation.
The known device is provided for laboratory operation, in which optimum test conditions are present and usable test results, even in the case of low sensitivity of the device, can be achieved. For practical use in dental diagnosis, however, it is necessary to increase the sensitivity of the device considerably in order to detect caries. Furthermore, the known device is difficult to handle, so that it is not suitable as a means of diagnosis for use with humans or animals.